The Stars and Stripes additionally states:

"P-3C aircraft were grounded three times in 2005 and 2006, but those aircraft have since returned to service, Davis said. He also said the Navy is confident the P-3C aircraft not affected by the grounding are safe to fly. The Navy has 161 P-3C Orion aircraft,...The average age...is 28 years...The oldest aircraft is 44 years old, and the youngest is 16 years old. The first squadron of the P-3C’s replacement, the P-8A Poseidon, is expected to stand up in 2013..."

While the article mentions 10 of the 39 are deployed it makes no mention of how many total are deployed. The P3C is a platform in search of a mission since the undersea threat has diminished significantly (but could soon rise as China flexes and Russia rearms)

And while structural fatigue will always be a problem for aircraft, and more so as the airframe ages, it is still should not always the ratioanl for replacing the aircraft with a more expensive version. To wit the B-52.

The KC-135 is still doing service and a telling statement made by a senior USAF officer went something like this: "The father of the last KC-135 pilot hasn't been born yet."